Up to now, hollow rotary drum processors have been heated by pumping hot water into and out of the drum as the drum is rotated. The hot water may be pumped into the drum and withdrawn from the drum at one end through a pair of co-axial pipes which are formed in a hub of the drum at one end. In another arrangement the hot water may be pumped into the drum through a tubular hub at one end, through and out of the drum at another end via another tubular hub. In both cases a reservoir of hot water must be provided as must a pump. Also there must be provision for sealing against leakage of liquid at the interface between the tubular hub or hubs of the drum and the static conduits leading to the pump and the reservoir.